(function () {
  var jQuery = window.$ = function() {
    // Intialize
  }
})()

var $ = (function() {
  function jQuery() {
    // Initialize
  }
  return jQuery
})()

npx rollup -f iife -n $ -o ./dist/jquery.js  ./src/jquery.js

var $ = (function (exports) {
    'use strict';
    function jQuery() {
        console.log('I am jQuery');
    }
    exports.jQuery = jQuery;
    Object.defineProperty(exports, '__esModule', { value: true });
    return exports;
})({});

<script src="./dist/jquery.js"></script>
<script>
    // test
    $()
</script>